Scoping Changes with Method Namespaces Alexandre Bergel ADAM Project, INRIA Futurs Lille, France
[email protected] Abstract. Size and complexity of software has reached a point where modular constructs provided by traditional object-oriented programming languages are not expressive enough. A typical situation is how to modify a legacy code without breaking its existing clients. We propose method namespaces as a visibility mechanism for behavioral refine- ments of classes (method addition and redefinition). New methods may be added and existing methods may be redefined in a method namespace. This results in a new version of a class accessible only within the defining method namespace. This mechanism, complementary to inheritance in object-orientation and tradi- tional packages, allows unanticipated changes while minimizing the impact on former code. Method Namespaces have been implemented in the Squeak Smalltalk system and has been successfully used to provide a translated version of a library without ad- versely impacting its original clients. We also provide benchmarks that demon- strate its application in a practical setting. 1 Introduction Managing evolution and changes is a critical part of the life cycle of all software sys- tems [BMZ+05, NDGL06]. In software, changes are modeled as a set of incremental code refinements such as class redefinition, method addition, and method redefinition. Class-based object-oriented programming languages (OOP) models code refinements with subclasses that contain behavioral differences. It appears that subclassing is well adapted when evolution is anticipated. For example, most design patterns and frame- works rely on class inheritance to express future anticipated adaptation and evolution. However, subclassing does not as easily help in expressing unanticipated software evo- lution [FF98a, BDN05b].